In a balanced woven wire conveyor belt, a longitudinally extending series of transversally extending spirals of wire, usually made of steel and steel alloys, is integrated into a longitudinally extending belt which is usually endless in the longitudinal direction, but has two transversally opposite, i.e., left and right, longitudinally running edges), by a longitudinally extending series of transversally extending rods, or bars also usually made of steel. In the series of spiral wires, alternate ones are spirally wound in a left-handed and right-handed spiraling sense and "skewered" in common on one rod, so that each spiral wire is skewered by two connecting rods, of which one leads and the other trails, assuming that the woven wire conveyor belt thereby constructed has a usual direction of advance in a longitudinal direction.
The main reason that alternate rows of spiral wires spiral in opposite senses is to prevent the assembled woven wire belting from tending to "walk" leftwards or rightwards as it runs in a longitudinal direction entrained about various driving, idling and tensioning rolls. The tendency of one row to cause the belt to walk to the left is immediately countered by the tendency of the succeeding row to cause the belt to walk to the right with the net effect that the belt tends to run essentially longitudinally.
The spiral wires are conventionally termed "flat spirals", because, looking at them endwise, they are not circular ring-shaped, but oval ring-shaped, because they have been "squashed" in a top-to-bottom thickness sense, so that each spiral is wider (in the lengthwise direction of the conveyor belt), than it is tall (in the thicknesswise direction of the conveyor belt).
Woven wire conveyor belts have been around for many years, likely for more years than anyone now working in the field. Early on, it was discovered that the performance of woven wire conveyor belting could be improved by "crimping" the connecting rods, i.e., causing them to be regularly undulatory along their lengths, so that individual coils of the spiral wires tended to seat, and to remain seated in respective individual dents, crimps, recesses or pockets in the crimp rods.
An ingenious way of creating the crimps in the connecting rods, discovered long ago, was to run the rods, during their manufacture, straight through the nip between two meshing gears that were made of harder more durable material than the rods, so that the rods came out looking something like a piece of gum does after it has been squashed between a person's back teeth. In the earliest examples of crimped connecting rod-type woven wire belting, the spiral wires individually have circular transverse cross-sectional figures (profiles) and the crimps in the crimp rods are "straight", i.e., precisely crosswise (i.e., essentially transversally) of the crimp rods. (In the industry, crimped connecting rods often are called "crimp rods".) This product is a definite improvement over flat spiral woven round wire conveyor belts with non-crimped rods, because the spiral turns do in fact seat in the crimp pockets on the rods. In fact, this form of construction has become an industry standard. It is believed that in somewhat over half of all woven wire conveyor belting sold these days, the flat spirals are made of round wire, and the connecting rods have straight crimps.
However, since each spiral turn passes around a respective connecting rod at an oblique angle, and the crimp notch is straight, only a limited-area point contact is formed between the spiral wire and the crimp rod. This results in a less-than-perfect seating of each spiral turn against the respective crimp rod and leads to significant (and undesirable) longitudinal stretching of the endless conveyor belt, particularly when the belt is used in high temperature and heavy load applications. (When a belt stretches, the excess length must be taken out, or taken up by using adjustable belt-tensioning means, so that neither the carrying run nor the return run will sag excessively. Excess belt length, not removed or properly taken up, can cause operating problems, including improper tracking of the belt on and around driving, idling and tensioning rolls.)
A major improvement in the conventional round wire/straight crimp woven wire belting was made by Fred Hooper, an employee of The Cambridge Wire Cloth Company, back in the 1950's. In that development, which is disclosed in U.S. Pat. No. 2,885,164, issued May 5, 1959, the transverse cross-sections of the flat spiral wires remained circular as before, but the connecting rods were run through slant-toothed gears during their manufacture, so that the crimp notches formed in alternately diametrically opposed sites on the crimp rods were oblique to the longitudinal axis of the crimp rods, with the angle of obliqueness of the crimps equalling the angle of spiraling of the coils of the spiral. The area of interfacial (i.e., superficial) contact between the spiral turns and the crimp rods was thereby substantially increased. As a result, such woven wire belts provide better seating of the spiral wires in the crimp notches, leading to straighter belt tracking and reduced belt stretch despite high temperature use (i.e., for use as product supports in continuous operations through tunnel-type baking and heat-treating ovens), during which the belts may be strongly tensioned in order to minimize product tipping and unwanted contact of the belt with nearby structures. This type of round wire/diagonal crimp woven wire conveyor belt has captured a significant segment of the market because of its superiority in relation to the theretofore conventional round wire/straight crimp woven wire conveyor belt. Nevertheless, it was not and is not considered to be a perfect solution. Two characteristics that this product has are sometimes considered to be unacceptable (or at least undesirable problems). These are, respectively, product-stability, and product-marking problems. Because conveyor belts made of the flat spirals nevertheless have many rounded upwardly presented profiles of individual spiral turns in their carrying runs, products, particularly ones that are tall and thin in their as-carried orientation, such as empty beverage can bodies, nail polish bottles and the like, are susceptible to tipping over, particularly if there is any jerkiness in the running of the belt. A domino effect can cause many items of the carried product to topple over when one does.
Now, imagine what it feels like to walk on a high wire in your bare feet. Totally aside from the fear factor, it's uncomfortable, because the wire tends to bite into the soles of your feet. That effect is partly due to the shape of the interfacial (superficial) contact between your foot and the wire, and partly due to the smallness of the area of the wire that must support all of your weight. A way of alleviating the pain immediately suggests itself (i.e., apart from not walking on the wire). The solution is to flatten the wire, so that the surface that it presents to the soles of your feet is both broader and flat.
Precisely this same sort of problem occurs in the transporting of certain products using woven wire conveyor belts, and heretofore, it has been solved in precisely the same way.
An example of the types of products that have been adversely affected by the impact of their weight on round wire profiles while being carried on woven wire conveyor belts are: individual blobs of cookie dough, chocolate-enrobed candy bars and similar products, and lehr-tempered beer bottles and similar products, in which the contact with the belting caused unacceptable (or at least undesirable) markings and distortions on the undersides of the individual product items.
A response to the product-indentation problem, was the invention of flat spiral woven wire conveyor belting in which the spiral wires were manufactured using "half-round" or "cotter-pin" wire of generally D-shaped transverse cross-sectional profile, oriented in the conveyor belt so that the flat side, the facet of the "D" was oriented vertically upwards in the carrying run of the belt.
In the half-round wire belts heretofore made (within the knowledge of the present inventors), the crimp rods all have had straight crimps, rather than diagonal crimps. Therefore, whereas a flatter surface was provided on the carrying run of the belt, for greater product stability and less product marking, the point contact of the spirals with the crimp notches gave the same disadvantages as the pre-Hooper product, i.e., they are oriented excessive stretch in high temperature and heavy load applications.
A further development was flat wire/flat straight crimp flat spiral woven wire conveyor belting, in which the spiral wires rather than being D-shaped in transverse cross-sectional shape, have two diametrically opposed facets, with intervening convexly profiled surface segments. Whereas the spiral wires in this known modification were easy to manufacture, and easier to keep properly oriented while being wound into spiral form, the flat crimp profile on the connecting rods saddled the resulting product with substantially the same excessive stretch problem as the original round wire/straight crimp product had.
It is possible that regular flat wire belting (flat both sides) was developed before cotter pin wire. At any rate, to the present inventors' knowledge, cotter pin wire has never been widely used in conveyor belts. Its use, as far as the present inventors know, has been restricted to wide, open mesh veneer belts, which are used for carrying wood panels through drying ovens.
In a further prior art development, the flat wire concept was successfully teamed up with the diagonal crimp concept, to provide a flat spiral, woven wire conveyor belt in which the crimp notches on the connecting rods, were flat and extended at oblique angles to the longitudinal axes of the connecting rods that precisely matched the angle and profile of the individual spiral turns of the spiral wires. This also was an improvement over the prior art, but still not a perfect solution. A remaining problem with this product is difficult to illustrate in a two-dimensional drawing, so the inventors must beg the indulgence of their interested readers in trying to visualize it:
As one tries to match each interface of the spiral wires more closely with the crimped connecting rods, a gap exists between the middle of each crimp notch and the middle of the turn of the spiral of the flat wire passing around it. The essential concept is something like a non-flat-footed person walking barefoot on a concrete floor. Their foot tends t make contact with the floor towards the front of their foot (i.e., their toes and the ball of their foot), and towards the rear of their foot (i.e., their heel), but not in the middle (i.e., their arch). On the belt, the flat on the wire, arching through the flat diagonal crimp notch tends to contact only at the two edges of the crimp notch and not in the middle. As a result, whereas the spiral wires are well seated in the crimp notches, use of the belt causes the crimp rods to rapidly become worn at the leading and trailing edges of the individual crimp notches, causing not only belt slackness that needs to be taken up, but also an early reduction in the cross-sectional area of the connecting rods available for carrying belt tension. Accordingly, the tensile load-carrying capacity of the belt can become diminished (compared to design or theoretical tensile load-carrying capacity) fairly early in the working life of the belt.
Currently, according to the belief of the present inventors, there is a substantial market demand for flattened wire conveyor belting that did not exist when the Hooper patent was taken out. Flat wire/flat diagonal crimp woven wire belt has been produced to try to meet this market demand, but, as indicated above, the interfacial gap caused by arching of flat over flat (has caused some customers or potential customers for this product to perceive it) as not being as good as the round wire/diagonal crimp product made in accordance with the Hooper patent. (Round wire passing through a flat diagonal crimp notch also arches free of contact with the middle of the notch, however to a significantly lesser degree, so that there is a significantly greater area of interfacial contact between the spiral wires and the connecting rods within the individual crimp notches of a well-designed, well-manufactured Hooper-type round wire/flat diagonal crimp woven wire conveyor belt, than within the crimp notches of a comparable flat wire/flat diagonal crimp woven wire conveyor belt.)